The present invention relates to a valve timing control system for an internal combustion engine, which performs variable control of opening and closing timing of an intake or exhaust engine valve in accordance with the engine operating conditions.
Typically, the valve timing control system controls opening and closing timing of an engine valve by controlling the phase of rotation of a crankshaft and a camshaft on a power transfer path from the crankshaft to the camshaft. Specifically, the system comprises a driving rotator coupled to the crankshaft through a timing chain and the like, a follower rotator coupled to the camshaft and to which the driving rotator is mounted to enable relative rotation as required, and a mounting-angle control mechanism interposed between the two rotators to control a mounting angle formed therebetween. Operating-force providing means provide an operating force to the mounting-angle control mechanism when required to change the phase of rotation of the crankshaft and the camshaft.
Various types of mounting-angle control mechanisms have been developed, one of which uses a helical gear to convert rectilinear operation of a hydraulic piston to rotary operation of the driving and follower rotators. Recently, a mounting-angle control mechanism using a link is proposed which has many advantages such as shortened axial length and less friction loss.
However, as will be described in detail hereinafter, the valve timing control system including a link as mounting-angle control mechanism raises a problem of occurrence of vibration and noise. Additionally, the system presents problems of an increase in the number of parts and thus a cost rise, a decrease in design flexibility of various system portions due to increased size and weight, and a unstableness of valve timing control during high-speed operation.
It is, therefore, an object of the present invention to provide a valve timing control system for an internal combustion engine, which contributes to achievement of smooth and quiet operation as well as a reduction in the number of parts and thus cost lowering and in system size and weight, an increase in design flexibility, and a stabilization of valve timing control.
The present invention provides generally a system for controlling a valve timing in an internal combustion engine, which comprises: a driving rotator rotated by a crankshaft of the engine; a follower rotator provided to a camshaft of the engine, the follower rotator receiving power from the driving rotator; a radial guide provided to one of the driving rotator and the follower rotator; an intermediate rotator arranged rotatable with respect to the driving rotator and the follower rotator, the intermediate rotator comprising a spiral guide in a face opposite to the radial guide; a link having a base end pivotally coupled to another of the driving rotator and the follower rotator at a position distant from a center of rotation thereof and a front end arranged swingably and comprising a first engagement engaged with the spiral guide and a second engagement engaged with the radial guide; and a device which provides to the intermediate rotator an operating force for rotation with respect to the driving rotator and the follower rotator, the device making radial displacement of the front end of the link along the radial guide with the first engagement engaged with the spiral guide, the radial displacement being converted into relative rotation of the driving rotator and the follower rotator through the link, wherein the first engagement has a center of engagement located on a swinging axis of the front end of the link.